Mystery surrounds the case of a soldier who started seeing the world backwards after being injured during battle.
Patient M was shot in the head by a gun-launched missile while fighting on the Valencian front during the Spanish Civil War in May 1938.
After being found lying on the floor, the wounded soldier miraculously survived without needing operations or special care.
But when he regained consciousness two weeks after the blast, he began to see things upside down in certain situations.
Born in a village in the Ciudad Real region of Spain, the soldier saw a terrifying backwards world when he was resting, without major stimuli.
Objects appeared in triplicate and tinged green while his hearing and touch was also inverted.
This meant for example that sounds and touches appeared in his mind on the opposite side, confusing his body from an opposite reality.
The peculiar case went on to inspire theories of the human brain catching the attention of one doctor in particular.
Dr Justo Gonzalo treated the 25-year-old at a nearby military hospital where tests showed the missile had partly destroyed the outer layers of his brain towards the back left hand side.
The Spanish Civil War was a brutal conflict which lasted from 1936 to 1939, ending with the Nationalist victory over the Republicans and the establishment of a dictatorship under Francisco Franco.
Patient M had been fighting on the side of the Republicans and was likely shot by an enemy Francoist soldier.
He was given his medical name by Dr Gonzalo who realised the unique case could illuminate the functioning of the human brain, reports El Pais.
Born in Barcelona in 1910, Dr Gonzalo survived the war and continued seeing Patient M for almost half a century after until his death in 1986.
The remarkable case was rediscovered when the researcher's daughter Isabel Gonzalo dusted off her father’s archives including hundreds of documents and photos.
Now a physicist and professor, she met Patient M during his visits to her family home and recalled how "M looked at his wristwatch from any direction to check the time."
During the 1930s, scientists were divided between those who saw the brain and a whole and those who drew hard boundaries between different brain regions.
Based on his work with Patient M, Dr Gonzalo suggested an intermediate hypothesis – the theory of brain dynamics whereby the organ works with different gradients.
Working at his Skull Trauma Centre, Dr Gonzalo met Patient M and hundreds of other wounded patients who had an astonishing adaptive capability, he remarked in his book Cerebral Dynamics.
The doctor wrote that M "had found his abnormalities strange when, for example, he saw men working upside down on a scaffold."
He added: "In general, the disturbances go completely or almost completely unnoticed to the wounded.
"Later when they discover them, they don’t seem to worry but rather consider them as something temporary that does not affect or compromise their daily life."
It was also noted that Patient M tended to downplay his symptoms: “They are things that sometimes appear in my vision.”
The soldier, whose identity was never made known, died in the late 1990s.
